1. Field of the Invention
This invention relates to a screwhead forming apparatus, more particularly to a screwhead forming apparatus in which an elongated blank is forged directly to form a screwhead according to the shape of the die cavity of a forging die set in such a manner that no waste is created.
2. Description of the Related Art
Referring to FIG. 1, a conventional screwhead forming apparatus 1 is shown to include a feeding mechanism 11 disposed on a machine bed 10, a blocking mechanism 12, and a cutting mechanism 13. When an elongated blank 2 is held on a chuck 130 and engages the blocking mechanism 12, a cutting member 131 cuts the blank 2 to form a blank section 20 of a predetermined length which is moved by a push pin 14 away from the cutting member 13. Then, the blank section 20 is sent to a forging die mechanism 15 which includes fixed tubular die members 150, 151, 152 and punch-moved die members 153, 154, 155. The die members 153, 154, 155 are driven by a flywheel (not shown) and a crank (not shown) to reciprocate relative to the die members 150, 151, 152. In the die mechanism 15, the blank section 20 (see FIG. 2A) projects from the tubular die member 150 and is forged by means of the punch-moved die member 153 to form a first semi-finished product 21 (see FIG. 2B) which is further forged by means of the die members 151, 154 to form a second semi-finished product 22 (see FIG. 2C) that is further dealt with by means of the die members 152, 155 to form a final product 23 (see FIG. 2D) with a screwhead 24 (see FIG. 2E). The final product 23 is then pushed out of the die member 152 by means of a pushing rod 156. It is understood that a large amount of waste, which is about 6 to 30% according to the size of the final product 23, is created in the process of forming the hexagonal head of the final product 23 (see FIG. 2D) from the second semi-finished product 22.
To save the material, it is intended that a screwhead can be formed directly by a die forging process whereby no material is cut off. In such a process, a spring is needed to press a movable die, which is carried on a punch rod, against a stationary die. In a case where the spring has a sufficient spring force to press firmly the movable die against the stationary die, the compressible length of the spring is too small to conform with the one-stroke travel of the punch rod during the die forging process. Conversely, in a case where the spring has a sufficient compressible length, the spring force of the spring is too small to press firmly the movable die against the stationary die. As a result, a single spring cannot be useful for forming a screwhead in a forging die set during one stroke of the punch rod.